1. Field of the Invention
The present invention relates to an electric power controlling method and apparatus, and more particularly, to a method of demanding/supplying a necessary electric power through self-adjusting operations between two devices coupled through a serial bus such as an Universal Serial Bus (USB).
2. Background of the Related Art
FIG. 1 shows a related art personal computer and several peripheral devices that are connected each other through an USB. In FIG. 1, the personal computer 100 acts like a host of the USB, and input devices such as an electronic pen 205, a mouse 204, etc. are connected to the host 100 through a hub 102 conducting a keyboard function and a hub 101 conducting monitor function. Audio input/output devices such as a speaker 203, a microphone 202, etc. are also connected to the host 100 through the hub 101 that conducts the monitor function, and various peripheral devices such as a telephone 201 and a hub repeater 200 are directly connected to the host 100.
The USB connecting a variety of devices each other has been standardized by mutual agreement among Intel, Microsoft, and other major companies to prevent possible communication failures, which might be caused by a variety of complicated connector interfaces. Therefore, most of personal computers currently support the USB standard.
The host 100 supporting the USB standard transforms an AC power to a DC power, which is fed to the hub repeater 200 as well as its own elements. The hub repeater 200 supplies the DC power from the host 100 to a detachable device 300, e.g., a Personal Digital Assistance (PDA), if connected through the USB. While the DC power is feeding, the detachable device 300 uses the DC power in charging its battery (not shown) or running the device.
Before supplying the detachable device 300 with a necessary electric power through the hub repeater 200, the host 100 communicates with the detachable device 300 through two signal lines of the USB to know how much electric power is demanded in the detachable device 300.
Thereafter, the host 100 measures how much electric power is being supplied to other connected peripheral devices, and determines whether it is possible for the host 100 to supply the electric power demand for the detachable device 300. If possible, the host 100 supplies the demanded electric power. If not possible, e.g., a remaining electric power is not enough to supply the electric power demand, the host 100 rejects the request of power supply in order to prevent interruption, instability of the electric power supply to other connected devices or the like.
However, if the electric power demand is rejected, the detachable device 300 resets a current connecting state immediately. Therefore, the detachable device 300 must be re-connected after being physically separated from the hub repeater 200 if the detachable device intends to make an electric power demand again.
When the detachable device 300 is re-connected to the host 100, the above-explained operations are conducted again. However, physical detaching and re-connecting work is time consuming and inefficient. Further, the physical detaching and re-connecting work is somewhat tedious because an USB port is usually equipped at the back of a device.